The shocking news of the assault on the U.S. Consulate in Benghazi on Tuesday brought personal grief to those who knew U.S. Ambassador Chris Stevens. The attackers killed him along with another diplomat and two State Department security officers.

Senator John McCain considered Stevens a friend and in a joint statement with Senators Lieberman and Graham called him “one of America's finest and bravest diplomats.”

Tonight Anderson Cooper asks McCain about Stevens’ work and legacy in Benghazi. They also talk about the U.S. mission in Libya, where some are concerned about the worsening security situation and al Qaeda’s growing presence.

McCain also responds to the controversy on the campaign trail that came after Mitt Romney criticized a statement released by the American Embassy in Cairo – made before the first protests happened. Romney accused the president of sympathizing with the killers.

McCain said he hasn’t paid much attention to the back-and-forth, but he told Anderson that he shares Romney’s argument that “this president is weak in his leadership.”

Watch a preview of their conversation and see more at 8 and 10 p.m. ET.